One can get radically different results by estimating the number of observant followers of every religion, the reason being that members of many ethnic groups often choose to self-identify as adherents to a certain religion for cultural reasons, although they would not fit any traditional religiousness criteria (church attendance, familiarity with basic dogmas of their faith). For example, even though 80% of ethnic Russians self-identify as Russian Orthodox, less than 10% of them attend church services more than once a month and only 2-4% are considered to be integrated into church life.
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